1. Field of the Invention
The present invention relates to a developing device driver for a color image forming apparatus, and a color image forming apparatus using the same. More particularly, the present invention relates to a developing device driver for a color image forming apparatus that sequentially drives a plurality of developing devices arranged at a predetermined interval from a photoconductive medium, and an image forming apparatus using the same.
2. Description of the Related Art
Typical image forming apparatuses such as a laser beam printer operate as follows. A light is projected on a photoconductive medium electrified to a certain potential to form an electrostatic latent image on the photoconductive medium. The electrostatic latent image is developed by developers having predetermined colors using a developing device, transferred onto a recording medium through a transfer medium such as a transfer belt, fixed onto the recording medium by a fixing device, and then discharged from the main body of the apparatus.
Color images are typically formed by using either a single-path or a multi-path method. A single-path method uses four laser scanning units (LSUs) and photoconductive mediums, and a multi-path method uses a single LSU and photoconductive medium.
FIG. 1 shows part of the structure of a conventional color image forming apparatus to explain the developing operation of the multi-path method.
Referring to FIG. 1, developing devices 5Y, 5M, 5C and 5K for four colors comprise developing rollers 6Y, 6M, 6C and 6K, respectively. In order to develop an electrostatic latent image, for example, a yellow image formed on a photoconductive drum 3 for the first time, a predetermined bias voltage is applied to the yellow developing roller 6Y, and the yellow developing roller 6Y is rotated by a developing unit driving motor (not shown). As a result, developer adhered to a surface of the yellow developing roller 6Y is transferred to the electrostatic latent image on the photoconductive drum 3. Then, the developed yellow image is transferred onto a transfer belt 7.
Next, another electrostatic latent image, for example, a magenta image is formed and developed. A predetermined developing bias voltage is applied to the magenta developing roller 6M, and the magenta developing roller 6M is driven to develop the electrostatic latent image on the photoconductive drum 3. The developed magenta image is transferred so that it overlaps the yellow image on the transfer belt 7. Cyan and black images are developed and transferred through the same processes, thereby producing a final color image on the transfer belt 7. The final color image formed on the transfer belt 7 is transferred to a recording medium P1 supplied between the transfer belt 7 and a transfer roller 9.
In FIG. 1, developing roller gears 8Y, 8M, 8C and 8K drive the developing rollers 6Y, 6M, 6C and 6K.
FIG. 2 is a perspective view showing a structure of a driver for the developing unit of FIG. 1.
Referring to FIG. 2, the developing roller gears 8Y, 8M, 8C and 8K are connected by intermediate gears 11Y, 11M, 11C and 11K, and the intermediate gears 11Y, 11M, 11C and 11K are supplied and cut off with power transmitted from a driving source (not shown) by electric clutches 13Y, 13M, 13C and 13K.
More specifically, when developing the yellow image, the yellow electric clutch 13Y is turned on, and the power of the motor is transmitted to drive the yellow intermediate gear 11Y. The power is transmitted to the yellow developing roller gear 8Y and accordingly, the yellow developing roller 6Y is driven. At this time, the developing bias voltage is applied to the yellow developing roller 6Y so that the developer attached to the surface of the yellow developing roller 6Y develops the electrostatic latent image formed on the photoconductive drum 3.
When driving the magenta developing roller 6M, the developing bias voltage applied to the yellow developing roller 6Y and the yellow electric clutch 13Y are turned off, and the developing bias voltage for the magenta image and the magenta electric clutch 13M are turned on. Therefore, the power of the driving source is transmitted to the magenta developing roller gear 8M to drive the magenta developing roller 6M.
The same processes are applied to develop the cyan and the black images.
The use of a plurality of electric clutches increase material cost and increase the overall size of the apparatus. Additionally, the electric clutch may slip, which produces a delay in the operational time. Therefore, the electric clutch may generate timing errors. Moreover, the electric clutch generates noise during the operation.
Accordingly, there is a need for a developing device driver for a color image forming apparatus which has a reduced number of parts, improved timing accuracy, and reduced noise.